1. Field of Invention
Exemplary aspects of the present invention relate to a development device and a process cartridge for use in an image forming apparatus. More particularly, the present invention relates to a development device and a process cartridge which form a toner image on a photoconductor by transferring a toner of a two-component developer on a development roller with an electric field.
2. Description of the Related Art
A two-component development device for use in an image forming apparatus includes a developer container containing a two-component developer including a toner and a carrier therein. The developer container includes a developer agitation conveyance member configured to agitate the two-component developer to obtain a uniform toner density and to convey the agitated two-component developer towards a developer carrying member having a magnetic pole therein. The surface of the developer carrying member carries the two-component developer thereon to an electrostatic latent image on an image carrying member, thereby developing the electrostatic latent image with the two-component developer to form a toner image.
Such a developing device typically includes an agitation unit collecting and agitating the two-component developer, which has been used for a development process at least once, so as to be mixed with an additional toner supplied. When the developer and the additionally supplied toner are not adequately mixed or agitated, an abnormal image such as an uneven image density can be formed. The degree of the agitation can be determined based on the toner consumption (i.e., the ratio of the toner consumed to the two-component developer). For example, in a high speed and small-sized two-component development device, the amount of toner consumption is large relative to the volume of the two-component developer. Therefore, the agitation unit needs to enhance the agitatability thereof.
A variety of methods of enhancing the agitatability of a developer agitation conveyance member have been proposed.
One example attempts to enhance functions of mixing and agitating a two-component developer having a toner and a carrier. In a development device using a two-component developer to develop an electrostatic latent image, a mixture state of the toner and the carrier therein can influence the image qualities. Therefore, this example offers proposals for enhancing the mixing and agitating functions.
In addition, a development device in which an electric field is formed on or at a location between a developer layer control member and a development region is proposed to enhance the chargeability of the toner or to allow toner particles to jump to obtain a high quality image.
Further, proposals such that the rotation speed of an agitation screw is increased and an agitation screw with an improved shape is used have been made to enhance the agitatability of an agitation unit.
Another example attempts to form an alternating electric field in an upstream side from a development region in a development device of an image forming apparatus to impart an appropriate charging quantity of the toner while reducing a mechanical stress.
However, such development devices require driving motors with large torque. In addition, the development devices apply a large amount of energy to the developer, resulting in acceleration of developer deterioration. Also, when the agitation unit performing high speed agitation is used, the shaft of an agitation member, etc. can be worn, resulting in deterioration of the durability of the development device.